They're great for marking small effects, or for marking conditions. We've got a load of red ones that we got from Coke bottles and use for denoting bloodied creatures... Just hang them around the mini's neck, or let it slip down around the base.
Genius. Seriously, genius idea! Plus, an excuse to drink unhealthy amounts of fizzy drinks! There is no downside. (I know, I know, my dentist would disagree...)